Now Playing: Majority of people with dangerously high cholesterol not taking medication
Now Playing: What does it mean to become a bone marrow donor?
Now Playing: Scheduling exercise time based on fitness goals
Now Playing: Obesity epidemic grows in adults; perhaps levels off in youth
Now Playing: ‘GMA’ Hot List: Study reveals how many minutes of exercise you need
Now Playing: Could a pill help with peanut allergies?
Now Playing: Could freezing the ‘hunger nerve’ be the secret to weight loss?
Now Playing: Health benefits of exercise in short burst or longer bouts similar, new study finds
Now Playing: New report warns of widespread ineffectiveness of lower back pain treatments
Now Playing: How a nutritionist organizes her refrigerator
Now Playing: Twins suffering from liver disease, transplant saves one but other dies
Now Playing: Children more likely than before to draw scientists as women, study shows
Now Playing: 1 in 3 young adults ride with impaired drivers, according to new study
Now Playing: Chewbacca tells boy he’s getting new heart
Now Playing: Exercise may help your heart appear younger, study finds
Now Playing: What to know about the new menopause hot flash medicine
Now Playing: ‘GMA’ Hot List: Your DASH diet questions answered
Now Playing: Emergency center trauma nurse loves singing to her patients dressed as a princess
Now Playing: Your DASH diet questions answered
Now Playing: Teacher’s ‘mental wellness’ books’ wish list goes viral
Sex Education, Gambling and other News